Method of making pistons



April 19, 1932. G. MICHEL.

METHOD OF MAKING PISTONS Fiied May 1o. 1927 ln/undo@ www@ abtofcmq Patented Apr. 19, 1932 UNITED STATES PATENT oFFlcE GILBERT MICHEL, OF BAGNEUX, FRANCE METHOD oF MAKING PI'sToNs Application led May 10, 1927, Serial No. 190,316, and in France July 29, 1926.

metals or alloys, in which the piston head or end portion 1s surrounded by a coating or' 5 casing of a strong hard metal, for instance steel, whereby the whole device will be suitably protected and its strength and resistance to wear increased.

In accordance with the present invention the light metal portion (including the piston head and the lower portion' of theskirt) is, for a considerable portion of its lengt?, held within a Ajacket of a harder and mo e durable metal, which is less subject to wear, and in the manner of assembling these, the metal of the skirt is pressed into holding re`- cesses in the inner face of the jacket, preferably while both of these are hot, and then the entire device is cooled, leaving the jacket rigidly bound upon the piston body.

Stated briefly, the invention consists of de- A forming the roughly forged piston body of light metal (such as magnesium or magnesium alloys) from the interior towards the eX- terior, upon the interior of a jacket of hard metal, having preferably inthe interior face some projections of dovetail shape, the jacket being advantageously initially placed into a matrix.

It is evident that this manner of procedure permits,-on the one hand, a considerable economy in power, since it is the light metal only which is deformed .and not the hard metal;

and on the other piston needing only a relatively slight eX- terior shaping and dressing, since the jacket will not have been deformed, especially if it has been held in a proper matrix which conforms to its exterior form.

The present invention relates particularly to a piston of which the larger portion consists of a light metal or alloy such as magnesium or an alloy of this metal, and the outer body (and optionally the bearing surface of the bosses) of a metal whose inechanical properties are superior to those of most light metals, at the high temperatures to which the pistons are ordinarily subjected when in use.

The piston head is particularly subject to hand, there is obtained av thermic conditions, and it hence must be given a sufficient thickness. To avoid increasing the weight of this element, the' piston head must necessarily consist of very light metals or alloys, such asmagnesium and its alloys. On the contrary, the outer body of the piston serves, in use, as a guide and is subjected to considerable friction, and hence must possess great strength and resistance to abrasion when hot, and should therefore preferably consist of a harder metal, for example steel.

The piston head may advantageously be made of magnesium or a magnesium alloy, and preferably should be subjected to a thermo-mechanical treatment to give the metal a fibrous structure and tol improve its thermo-mechanical properties. ,This treatment may be obtained by forging, die-pressing, stamping, embossing or the like. I prefer to employ the process speciiied in French Patent No. 607,622, filed on the 7th of March `1925.

Preferably the portion, i. e. piston cast or otherwise made cast) from magnesium. This can then be trimmed, e. g. the skirt or a portion of the lengthof the skirt, may then beturned in a lathe, to give a smooth cylindrical surface. This is then placed Within the sleeve, of steel or the like, which entire assemblage is then heated in a matrix. The Askirt is then eX- panded, e. g. by rolling the inside of the same, to force light metal into the dovetails which are located on sleeve.

0r. the invention whole of the light metal head and',- skirt, is first l may be carried into eifect by separately constructing the said outer. body (sleeve) ofthe piston, of strong metal, provided on its interior face with suitable dovetails and in also constructing a blank for the piston head in magnesium or any alloy of this metal. The outer body is then iitted in the` hot state, upon the rest of the piston, with or without preliminary trimming of the lattver on its exterior, and the whole. device may be completed by the above described outward pressing' or like process. This preliminary trimming may consist of (i. e. forged or diethe interior surface of the turning the skirt, to give same a substantially smooth surface. i

The appended. drawings show by way of i example an embodimentJ of the invention.

. piston together.

The said outer body is first placed in the mold or matrixat the proper temperature, and the blank for the cylinderhead which consists of magnesium is now hot pressed at a high pressure upon the interior of said outer body, by deformation from the interior to theexterior (viz. outwardly), according .to the arrows f1 and f2. In this example, the bearing partsA 4 for the wrist pin ar formed in the magnesium portion of the skirt.

The device must be so arranged that the said outerbody will fit tightly upon the main part of the piston.

The present invention is not limited to the case in which the light metal of the device has magnesium as a base, and the said metal may be replaced by any -other light metal', especially -by metals which will assume a fibrous struct-ure when subjected to the mechanical operations as stated above.

In the appended claims, the term metal includes simple metals and alloys.

I claim:

l. Process of manufacturing pistons which comprises placing around a preformed light metal piston, a jacket of hard wear-resisting metal, having recesses upon its interior face,

. deforming said light metal by pressure from the interior towards the exterior, so that the light'metal iowsvback into .said recesses ofsaid jacket, and thus securely oining the jacket to the light metal piston. 2. Process of manufacturing pistons which comprises placing around a preformed light metal piston, a jacket of hard Wear-resisting metal, having recesses upon its interior face, deforming said light metal by pressure from the interior towards the exterior, so that the light meta-l flows back into said recesses of said jacket, and thus securely joining the jacket to the light metal piston and allowing the casing to cool upon said light metal core. 3. Process according to claim l, in which the operation of deformation of the light signature.

l GILBERT MICHEL.

metal by pressure is made at a relatively high Y temperature, but less than the temperature of softening of the light metal. 

